1. Field of the Invention
The invention relates to methods for measuring a growth rate of a carbon nanotube.
2. Discussion of Related Art
Carbon nanotubes (also herein refereed to as CNTs) are very small tube-shaped structures essentially having a composition of a graphite sheet in a tubular form. Carbon nanotubes have interesting and potentially useful electrical and mechanical properties and offer potential for various uses in electronic devices. Carbon nanotubes also feature extremely high electrical conductivity, very small diameters (much less than 100 nanometers), large aspect ratios (i.e. length/diameter ratios) (greater than 1000), and a tip-surface area near the theoretical limit (the smaller the tip-surface area, the more concentrated the electric field, and the greater the field enhancement factor). These features make carbon nanotubes ideal candidates for electron field emitters, white light sources, lithium secondary batteries, hydrogen storage cells, transistors, and cathode ray tubes (CRTs).
Generally, there are three methods for manufacturing carbon nanotubes. The first method is the arc discharge method, which was first discovered and reported in an article by Sumio Iijima, entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). The second method is the laser ablation method, which was reported in an article by T. W. Ebbesen et al., entitled “Large-scale Synthesis of Carbon Nanotubes” (Nature, Vol. 358, 1992, pp. 220). The third method is the chemical vapor deposition (CVD) method, which was reported in an article by W. Z. Li, entitled “Large-scale Synthesis of Aligned Carbon Nanotubes” (Science, Vol. 274, 1996, pp. 1701).
In order to use the carbon nanotubes more widely and more effectively, it is necessary to implement a controlled growth of the carbon nanotubes with desired structural parameters. Thus, it is pressing to unravel an underlying growth mechanism of the carbon nanotubes. On the road toward unraveling the growth mechanisms of the carbon nanotubes, it is of vital importance to study the growth kinetics of the carbon nanotubes. The progress in the synthesis of a CNT array gave a convenience of studying the growth kinetics of the carbon nanotubes by measuring a height of the CNT array. This is because the CNT array is a self-ordered structure, and the carbon nanotubes of the CNT array are nearly parallel-aligned.
The above-mentioned arc discharge method and laser ablation method can't synthesize CNT arrays, while the above-mentioned CVD method can synthesize CNT arrays. However, when adopting the conventional CVD method to synthesize a CNT array, the difficulty is that people do not readily know when the carbon nanotubes start their growth and when the growth has ceased. Furthermore, people can't easily distinguish whether the carbon nanotubes are formed in the tip-growth mode or the root-growth mode. Still furthermore, the growth rates of the carbon nanotubes at different temperatures can't be readily measured.
What is needed, therefore, is a method for readily measuring a growth rate of a carbon nanotube.